Preheat the oven to 170°C and grease a large muffin tray.
Using electric beaters or a mixer, beat together the butter, sugar, almonds and vanilla, for 10 minutes or until creamy and pale.
Add the eggs one at a time, beating after each addition.
Sift in the flour & baking powder, then add the ground pistachios. Gently fold them in, being careful not to over mix. Finally, fold in the sour cream.
Pour into the muffin moulds and bake for 30 minutes or until you can insert a knife and it comes out clean.
Remove from the moulds and allow to cool.